题目描述

C++代码

样例

#include<iostream>
#include<algorithm>
#include<vector>
#include<unordered_map>
using namespace std;
int main()
{
    int n;
    cin >> n;
    vector<int> vc(n);
    vector<int> v(n);
    unordered_map<int, int> mp;
    bool vis = false;
    int ans = -1;
    for (int i = 0; i < n; i++)
    {
        cin >> vc[i];
        mp[vc[i]]++;
        if (mp[vc[i]] == 1)
        {
            v.push_back(vc[i]);
        }
    }
    for (int i = 0; i < v.size(); i++)
    {
        if (mp[v[i]] == 1)
        {
            ans = v[i];
            break;
        }
    }
    if (ans != -1) {
        cout << ans;
    }
    else {
        cout << "None";
    }
    return 0;
}